This invention relates generally to exercise and rehabilitation systems and methods and, more specifically, to an active isokinetic exercise and rehabilitation system wherein isokinetic velocity is maintained in response to position of and torque applied to a patient attachment unit.
Research conducted over the past decade has demonstrated the value of isokinetic exercise from the standpoint of rehabilitating injured human joints and associated muscle groups as well as training joints and muscle groups for improvement of human performance. The term "isokinetic" refers to the exercise concept that involves restricting the movement of a portion of the body about a particular anatomical axis of rotation to a constant rotational velocity. This is achieved by applying an accommodating resistive force to the contracting muscle. This resistive force changes in value throughout the range of motion of the limb in a manner which opposes the varying amount of force that the associated muscle group is able to generate.
The observation that the amount of force which a muscle group generates varies throughout the range of motion of the associated joint may be explained in terms of anatomical axis of rotation (i.e., a variable biological lever length advantage), enzymatic profile (i.e., intracellular contractile and metabolic protein composition), musculo-tendinous length tension relation and ballistic considerations. An example of this phenomenon can be shown in the knee joint extension during which the quadriceps muscle is seen to develop peak torque at about the midrange of rotation.
Conventional methods of "free weights" exercise require the muscle to act against a load which cannot be greater than the torque developed at the weakest point in the range of motion of the joint. Thus, with free weights the muscle operates at a reasonable work load in only a small portion of the overall range of motion, and the muscle does not experience optimal loading at the stronger points in the range of motion.
Semi-accommodating resistance exercise, wherein the load on the muscle is biased and semi-variable, is provided in some cam-based exercise systems. However, these systems are at best approximations to the variations in force generated by the particular muscle groups sampled from a cross-section of individuals. This approximation of variable force generation, which may be visualized as a quasi bell-shaped curve of force plotted against degrees of range of motion, is used to shape a cam to control application of the resistive force in a semi-accommodating, semi-variable manner.
Isokinetic exercise systems, on the other hand, create a variable force which imitates and opposes the variable force generated by the involved muscle group as the limb moves throughout its range of motion. In this type of system, the rotational velocity of the lever arm or other patient attachment unit to which the limb is attached is constrained to a maximum permitted value, and any force exerted by the limb which tends to accelerate the lever arm beyond that maximum value is matched with an accommodating resistance. Accordingly, the muscle group involved operates at its optimal tension development throughout the entire range of motion. The net rehabilitation benefit or the net gain in human performance using this technique is substantially greater than that achieved with conventional exercise techniques.
Isokinetic exercise systems may be passive or active. A passive exercise system is shown in U.S. Pat. No. 4,601,468 issued to Bond, et al. An active exercise system is exemplified in U.S. Pat. No. 4,628,910 issued to Krukowski. In these systems, a servo motor is mechanically coupled to a movable arm against which a force can be applied. A sensing device senses the force applied to the arm and produces a load signal corresponding thereto. A tachometer produces a velocity signal corresponding to the velocity of the arm, and a closed loop velocity servo feedback circuit controls the motor in response to the load signal and the velocity signal so that the arm has a constant resistive torque applied thereto and/or has its velocity regulated regardless of the force applied to the arm.
However, velocity servo control loops used in known active exercise systems require adjustment of analog signals which, in turn, are subject to electrical perturbations.